Decoction Mashing: Techniques

Looking to make some malty wort the old school way? Try decoction mashing.

As we all know, mashing is the process in which crushed malts are soaked in hot water, resulting in the conversion of the starch in the malt to simpler sugars. The idea is conceptually simple, but in practice there are a variety of ways to go about it. Historically, new methods of mashing have arisen to deal with new technologies, new ingredients and increases in malt quality.

Common types of mashing

Today, most malts are well modified and respond well to a single infusion mash when an all-malt beer is being brewed. The mash temperature of a single infusion mash is almost always in the 148–162 °F (64–72 °C) range. Step infusion mashes, in which the mash is rested at two or more temperatures, may be accomplished by heating the mash directly or adding infusions of boiling water to raise the temperature between rests. A common single step mash is one with a rest in the beta-glucanase range (113–122 °F/45–50 °C) followed by a rest in the saccharification range (148–162 °F/64–72 °C).

If adjuncts such as corn grits or rice are used, a double or cereal mash is employed. In essence, the cereal adjunct is cooked separately to rupture the starch granules in the grains. Then the cereal mash is returned to the main mash, which is composed of barley malt with high enzymatic content. (The type of malt used in conjunction with large amounts of adjunct is usually 6-row malt. Purified amylase enzymes may also be added to aid with starch conversion.) Because the cereals are added to the main mash at near-boiling temperatures, the temperature of the combined mash increases and double mashes are thus stepped mashes. (Flaked or torrefied grains are adjuncts that can simply be stirred into a mash.)

A decoction mash is a step mash that is performed by removing a portion of the mash, boiling it and returning it to the main mash. Traditionally, decoction mashing was used to get the most out of malt that was not produced to today’s levels of modification. In the past, malt was both less modified and more variable with respect to degree of modification.

Decoction mashes may involve more than one cycle of separating (or pulling) a decoction, boiling it and returning to the mash. The traditional type of decoction mashing is a triple decoction mash, in which decoctions are boiled and returned to the main mash three times. As such there are four temperature rests, one at the temperature the grains are mashed in at and one after each decoction. Decoction mashing was developed before the advent of thermometers, and the standard triple decoction mash may owe many of its features to this fact.

Pros and cons

Some brewers argue that a decoction mash yields a desirable malt characteristic in beer, particularly German and Czech-style lagers, — such as Pilsners, bocks, doppelbocks and Oktoberfests —that other mashing methods cannot duplicate. Pilsner Urquell is an example of a beer that is decoction mashed.

Other brewers see decoction mashing as a huge waste of time and energy (as in BTUs), and some dispute the contention that decoction mashing produces a character that cannot be obtained any other way. A triple decoction mash is very time and energy consuming and most commercial breweries that once performed this type of mash have either shortened their mashes to double decoction or single decoction mashes, or have begun infusion mashing. Most brewers, however, will agree on the following points.

Decoction mashing results in some melanoidin production. Melanoidins are red-brown, aromatic compounds formed by reactions between amino acids and sugars. They are formed at temperatures over 194 °F (90 °C). Both Munich malts and — big surprise — melanoidin malts are rich in melanoidins, and some brewers argue you can mimic the effects of a decoction mash by adding a portion of these malts to your grist. In pale beers, brewers attempt to minimize melanoidin production. In darker beers, they look for ways to increase it. Since parts of the mash are boiled in a decoction mash, and wort boils at around around 215 °F (102 °C), melanoidins are produced. The degree to which they are produced depends on how intensely the decoctions are boiled and the levels of protein modification (and hence the availability of amino acids) in the malt.

Decoction mashing extracts more tannins than an infusion mash. Along with gelating the starch, boiling the mash extracts husk compounds, including polyphenols (tannins). The level of tannin extraction, however, is fairly low and some maintain that this low level actually benefits the flavor of the beer. If a low, pleasing amount of tannin extraction is a piece of “decoction mash character,” then simply adding Munich or melanoidin malt would not capture that character exactly.

Homebrewers used to infusion mashing may wonder how a decoction could be boiled without extracting a large amount of tannins and yielding a very astringent beer. After all, when lautering, they are repeatedly told that their grain bed temperature should never exceed 170 °C (77 °C). The key to understanding this apparent discrepancy is understanding when tannins are soluble in wort. Increased heat and increased pH both favor tannin extraction. At lower pH values, such as those found in a thick mash, tannin extraction from grain husks is minimal even at boiling temperatures. At higher pH values — such as those in a grain bed that has been extensively sparged — excess tannin extraction occurs at a much lower temperature.

Decoction mashing inactivates some of the enzymes in a mash. Enzymes are proteins (strings of amino acids) that are folded into a specific three-dimensional shape. The shape of the enzyme determines its function. When heated, enzymes unravel (or denature, in the lingo). Different enzymes denature at different temperatures because they assume different shapes and some are “cross-linked” by sulphur bridges that stabilize their structure. Boiling temperatures are sufficient to denature almost all enzymes and thus boiling the mash inactivates any enzymes that are useful in brewing. In decoction mashing, only roughly a third of the mash is boiled at each decoction and enzymes from the unboiled mash compensate for those denatured in the decoction boil.

Besides boiling of a portion of the mash, decoction mashing involves a lot of stirring and can result in an increased yield for many brewers. In a home brewery, a decoction mash is likely to give the brewer a better yield compared to an unstirred single infusion mash. My efficiency typically jumps by around 5% when I decoct.

Decoction mashing also results in increased removal of dimethyl sulfide (DMS), more intensive gelation of starch and less protein breakdown in the boiled portion of the mash. (Fewer proteins are degraded because the mash temperature of the decoction moves more quickly through the rests where proteinases are active than in the mash as a whole.)

Triple decoction mash

Although it takes some time and planning, it is certainly very possible to perform a triple decoction mash in a homebrewery. It does help, however, to have a brewing partner as you need to monitor what is going on in two mashes at the same time and the boiled mash needs nearly constant stirring.

Some maltsters sell less modified (or “undermodified”) malts, and these are a good malt choice when doing a triple decoction mash. You can triple decoct using modern, well modified malts, but you may want to consider shortening some of the rests. At a minimum, it will save you time.

A triple decoction mash begins with a mash in at around 99 °F (37 °C). The mash thickness for pale beers is usually around 2.3–2.6 quarts of water per pound of grain (4.8–5.4 L/kg). For darker beers, a stiffer mash — around 1.4– 1.9 qts./lb. (3.0–4.0 L/kg) — is used. Infusion mashes are generally thicker than both of these. As an option, the decoction mash can be mashed in very thickly at ambient temperature, then brought to the correct mash temperature and thickness with an infusion of hot water. I mash in my kettle as this makes it easy to apply direct heat if I need to make a slight temperature correction.

These days the explanation for this temperature is often that it activates the enzyme phytase, which lowers mash pH. Of course, decoction mashing was pioneered long before enzymes were discovered. (In fact, it was before things like cells and molecules — things you would need to understand before you could fathom the idea of an enzyme — were discovered. The choice of this temperature may be because it is easy to judge. At human body temperature — which varies, but hovers around 99 °F (37 °C) — water feels neither hot nor cold. Mashing in at this temperature may have been an adaptation to the lack of thermometers. (Another pre-thermometer way to achieve reasonably consistent water temperatures is to mix a fixed ratio of boiled water — which must be around 212 °F (100 °C), depending on elevation — and well water — which hovers around 54 °F (12 °C) at most locations.

Next, the brewer “pulls a decoction.” In other words, he scoops out the thickest one-third of the mash and heats it in a separate pot. You can do this after a short rest, around 15 minutes, or you can let the rest sit at 99 °F (37 °C) for (literally) hours. (If you want phytase to produce a noticeable change in mash pH, you may indeed need to rest here for hours.) Heat the decoction to 150 °F (66 °C) and let this rest for 15–20 minutes. This allows some starch conversion to occur before the decoction is boiled and the enzymes destroyed. In a modern, well-modified malt, the decoction portion of the mash may completely convert, or nearly so, at this step. Next, the decoction is heated to a boil. For pale beers, the decoction is boiled for 15 minutes. Dark beers, in which more melanoidin production is desired, are boiled longer — up to 40 minutes. I usually boil my decoctions on my kitchen stove, as I worry that I will heat the mash too quickly and scorch it if I use one of my propane burners.

While any of the decoctions are being boiled, you must stir nearly constantly to prevent scorching. Although not traditional practice, I almost always add a pinch of calcium — either gypsum or calcium chloride — to the boiled decoction, to help the boiled mash achieve a desirably low pH.

After the first decoction is boiled, it is returned to the main mash, establishing a mash temperature around 125 °F (52 °C). (These days, we’d describe this rest as activating beta-glucanase. Older sources would likely call it a protein rest. With well modified malt, you may choose to proceed directly to the next decoction.) After a variable amount of time — from roughly 15–30 minutes — a second decoction is pulled and boiled. Like the first decoction, this should be the thickest one-third of the mash. This decoction is boiled for 15–30 minutes and returned to the mash.

Once the second decoction is returned, the mash temperature should settle to around 149 °F (65 °C). Traditionally, the mash was allowed to rest for about an hour at this point. At this temperature, of course, starch is being converted into maltose and other sugars. If you are using a modern, well-modified malt, you can shorten this rest to 30 minutes (or shorter, if you confirm conversion with an iodine test).

After your conversion rest, a final decoction is pulled, boiled for 15–30 minutes and returned to the main mash for a mash out temperature around 170 °F (77 °C). A mash-out makes lautering easier — and lautering would likely have been more variable with historical malts. These days, we also know it brings most enzyme activity to a halt, “fixing” your carbohydrate profile. Now, what may be six hours later, you are ready to begin recirculation and lautering.

Other decoction programs

Shorter decoction mashes exist, both double and single. By varying the size of the decoction you pull and your mash-in temperature, you can come up with just about any set of rests you would like. If you mash in your kettle, you can also combine direct heat for steps or ramps within your decoction mash.

Schmitz process

One interesting single decoction program is the Schmitz process. This combines directly heated steps with one decoction to complete a step mash.

For a single decoction mash using the Schmitz process, mash in at 122 °F (50 °C), then begin heating the mash to 150 °F (66 °C). Stir the mash as you heat. If you are making a dark beer, a long rest at ambient temperature — in German, a vormaischverfahren — may proceed heating the mash to mash-in temperature.

When you reach 150 °F (66 °C), let the mash solids settle. Once they are settled, carefully scoop out the liquid part of the mash — the part with the dissolved enzymes — and put it in another kettle. Keep this liquid at 150 °F (66 °C).

Boil the mash solids (and surrounding liquid) that were left behind for 15–30 minutes. Next, cool the mash back down to the point that, when you combine it with the liquids you are reserving, your temperature comes to rest within the saccharification range.

Obviously, you would cool the grains down to 150 °F (66 °C ) if you wanted the recombined mash temperature to be 150 °F (6 °C). If you wanted a higher temperature, cool the grains less. The exact amount depends on the proportion of water you scooped out to the proportion of grain left behind.

To cool your decoction, use a copper coil immersion chiller. Once you’ve added back the liquid part of the mash, you can use either direct heat or your immersion cooler to correct your temperature, if needed.

The first time you try a decoction mash, take good notes regarding the volumes of the decoctions you pull and the temperatures your recombined mashes settle in to. Use this information to tweak your plans for subsequent brewdays.

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